Motion-free en face OCT Angiography and Pigment Imaging based on Modified Lissajous Scan

Abstract

Purpose : Due to the eye motion during data acquisition, en face optical coherence tomography angiography (OCT-A) imaging is prone to motion artifacts including blood vessels discontinuities, missing areas, and morphological distortions. These artifacts can significantly disturb the clinical observation of ocular vasculature. To provide motion corrected en face OCT-A images, we developed a modified Lissajous scan method for OCT-A and motion correction algorithm tailored for the modified Lissajous scan.

Methods : ONH and macula of 3 normal eyes were scanned 2 times by the modified Lissajous scan with 6 mm × 6 mm transversal area in 5.2 s, which is compatible for OCT-A measurement. The modified Lissajous scan was designed to sequentially scan the same location twice as keeping the smoothness of the scan. The data were processed by the tailored motion correction algorithm.
Although this method is compatible with standard OCT devices, it was implemented on a Jones matrix OCT with a probe wavelength of 1-µm and a scanning speed of 100,000 A-lines/s. Owing to its polarization measurement capability, the en face composition of OCT-A and polarization uniformity, which is sensitive to melanin, is created.

Results : We compare en face images before (a, d) and after (b, e) motion correction. These images are overlaid on manually co-registered SLO images (c, f). The images before motion correction (a, d) shows significant blurring and ghost vessels. On the other hand, the motion corrected images do not show blurring and ghost vessels (b, e), and are perfectly co-registered with SLO images (c, f). Fig. (g) shows a case with an eye blink (horizontal dark line), where vertical axis is Lissajous cycle index and horizontal axis is time in the cycle. Despite of the blink, the motion corrected en face image shows the clear vessels (h) and perfect co-registration with SLO (i). The corrected en face image shows clear vessels for 5 of 6 volumes of ONH and 6 of 6 volumes of the macula, although 4 of 12 volumes had vignetting and some residual artifacts.

Conclusions : The motion-corrected en face OCT-A was demonstrated. This method can provide true ocular vascular morphology.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Figure: (a, d) are before motion correction and (b, e, h) are after motion correction. (c, f, i) are comparison of motion corrected images (b, e, h) with SLO. (g) is a blinking en face image before remapping.